\begin{tikzpicture}
    \tkzDefPoints{0/0/O, 2.5/0/D}
    \tkzDefPoint(80:2.5){A}
    \tkzDefPoint(60:2.5){C}
    \tkzDefPoint(20:2.5){B}

    \tkzDrawSegments(O,A  O,B  O,C  O,D)
    \tkzMarkAngles[size=0.6](C,O,A  D,O,B)
    \tkzLabelAngle[pos=0.9](C,O,A){$1$}
    \tkzLabelAngle[pos=0.9](D,O,B){$2$}
    \tkzLabelPoints[below](O,D)
    \tkzLabelPoints[right](A,B,C)
\end{tikzpicture}

